Marijuana smoking has been implicated as a risk factor in cancer due to the known carcinogens in marijuana smoke. However, dosage exposure is very difficult to quantitate with an agent administered via the inhalation route. The present project proposes to utilize newly developed technologies for measurement of smoke puffing and inhalation to 1) identify the behavioral smoking parameters (e.g. puff volume, lung exposure time that are important for determining effective dosages smoked marijuana, 2) determine the plasma THC levels associated with various dosing techniques and parameters and 3) characterize smoking styles and dosage exposure of several relevant user populations. Initial studies will determine biological dosage exposure associated with ad lib smoking of marijuana cigarette containing a wide range of THC concentrations (1%-4% THC) in moderate users (Exp.1), determine biological dosage exposure associated with paced smoking procedures commonly used in research laboratories (Exp 2), and determine whether smoking styles and/or exposure levels change systematically over repeated exposure to marijuana cigarettes of a give potency (Exp.3). A subsequent series of 5 studies will train subjects to experimentally control and manipulate smoking behavior; plasma THC exposure levels will be used to identify the components of marijuana smoking behavior that contribute to dosage exposure variation. The 5 behavioral components to be separately manipulated in each experiment are: number of puffs (Exp.4) puff volume (Exp.5), puff spacing (Exp. 6), inhalation duration or lung exposure time (Exp.7) and inhalation volume (Exp.8). A final series of studies will examine individual subject differences in smoking behavior to determine how these translate into characteristic dosage exposures. The subject characteristics to be examined are typical use frequency (heavy versus light use; Exp.9), concurrent tobacco use (Exp.10) and gender (Exp.11). Overall, these studies will provide valuable information about the behavioral determinants of marijuana dosing via the inhalation route and about individual differences in smoking styles and dosage exposure. The data to be obtained will be important for understanding the relationship between smoking behaviors and dosage exposure (plasma THC) and for beginning to delineate relative health risks of marijuana smoking among different user groups.